(a) Field of the Invention
The present invention relates to electric shutters and more particularly to improvements in an electric shutter of a program type.
(B) Description of the Prior Art
In a conventional electric shutter, as means of opening and closing shutter blades, a first actuating force source for opening the shutter blades and a second actuating force source for closing the shutter blades are provided separately from each other so as to be separately tensioned when the shutter is cocked. Therefore, when the shutter is released, first the shutter blades will be opened by the first actuating force source, then the closing member will be unlocked by the action of an electromagnet after the lapse of a proper exposure time by the action of a well known exposure time controlling circuit including CdS or the like and the shutter blades will be closed by the second actuating force source to complete one photographing. However, with such arrangement, there have been defects that, as the actuating force sources, for example, springs are arranged in two places, the arrangement is complicated and the strength of the second actuating force source must also be adjusted in response to the strength of the first actuating force source.
Further, in an electric shutter, in order that even a comparatively small magnetic force of an electromagnet may positively attract and hold an armature lever member, it is already suggested as disclosed in Japanese Utility Model Publication No. 24466/69 to keep a spring in the direction of being pressed in contact with the electromagnet acting on the armature lever member. However, there has been a defect that, after the electromagnet is de-energized, the shutter blade closing actuating member will have to move always against the spring force, the closing action will become unstable and the amount of exposure will fluctuate. On the other hand, it is suggested as disclosed in Japanese Utility Model Opening No. 62034/74 to displace the above mentioned spring to an independent position from the armature lever member by means of a releasing member. However, this has a defect that an increase in the releasing stroke and releasing force will result.
Particularly a blade opening and closing member in an electric shutter of a program type will operate in a predetermined entire range only when the diaphragm aperture is fully opened but will be returned from the course of the displacement otherwise. Therefore, for a photographing by using a flashing means, a synchroswitch has been made to be of a moving contact type in response to the diaphragm aperture or a flashing circuit has been made to be controlled through SCR by a de-energizing signal for the elctromagnet. However, there have been defects that the mechanism will be complicated and will not be properly operated at a low voltage.